Fuel-pumping system with vortex-type flow resistor

ABSTRACT

A fuel-pumping system for a gas turbine engine includes a jet pump in the fuel tank, a boost pump, a pressure pump, and a fuel control to control the fuel supply from the pressure pump to the engine. The jet pump is energized by fuel diverted from the outlet of the pressure pump through a static vortex-type flowresisting device having a pressure drop proportional to flow raised to a power greater than two. This device reduces the amount of increase in fuel returned to the jet pump which would otherwise occur under high-pressure discharge conditions of the pressure pump.

, United States Patent VORTEX-TYPE FLOW RESISTOR Alfred M. Suggs,Indianapolis, Ind.

General Motors Corporation, Mich.

June 4, 1970 Inventor:

Assignee: Detroit,

Int. Cl. ..F02c 9/10 Field ofSearch 60/3928; l37/569,565, 81.5

References Cited UNITED STATES PATENTS 10/1969 Rupertf. ..l37/81.51/1968 Rupert..... .60/39.28 UX 5/1970 Chow ..l37/81.5

12/1970 Freeman ..137/81.5

Suggs 51 Feb. 29, 1972 j [54] FUEL-PUMPING SYSTEM WITH FOREIGN PATENTSOR APPLICATIONS 726,496 10/ 1942 Germany ..137/569 PrimaryExaminer-Clarence R. Gordon AttorneyPaul Fitzpatrick and Jean L.Carpenter [57] ABSTRACT A fuel-pumping system for a gas turbine engineincludes a jet pump in the fuel tank, a boost pump, a pressure pump, anda fuel control to control the fuel supply from the pressure pump to theengine. The jet pump is energized by fuel diverted from the outlet ofthe pressure pump through a static vortex-type flow-resisting devicehaving a pressure drop proportional to flow raised to a power greaterthan two. This device reduces the amount of increase in fuel returned tothe jet pump which would otherwise occur under high-pressure dischargeconditions of the pressure pump.

5 Claims, 2 Drawing Figures ENGINE FUEL E CONTROL 7 ENGINE Patented Feb.29-, 1972 FUEL CONTROL INVENTUR. fllfim ZZZ 5&5

FUEL-PUMPING SYSTEM 'WITH VORTEX-TYPE FLOW RESISTOR The inventionhereindescribed was made in the course of work under a Contract or subcontractthereunder with the Department of Defense.

DESCRIPTION My invention relates to fuel-pumping systems such, forexample, as are employed to supply fuel to aircraft gas turbine enginesand particularly to fuel systems of the sort in which a jet pump in thefuel tank is employed to provide a small pressure head in the fuelflowing from the reservoir to the fuelpumping devices of the engine toprevent cavitation in the fuel pumps.

Where a jet pump is so used, it is energized by fuel under pressurediverted from the main fuel pump of the engine. The flow must besufficient to secure adequate inlet pressure at the engine driven pumpsat a low fuel flow rate and corresponding relatively low pressure offuel delivered to the engine. As the engine fuel consumption increases,and with it the pressure of the fuel supplied, the flow to energize thejet pump increases. Normally, it will increase beyond what is needed, sothat there is a-wasteof pumped fuel under pressure.

According to my invention, a flow resisting or regulating device. of astatic vortex flow type is interposed in the energizing fuel line to thejet pump. Such a device has the characteristic that the drop in pressurethrough the flow resistor is proportional to flow rate as to a powergreater than two; for example, the exponent may be of the order of 2.4.With such a device, the increase in flow at higher pressures is lessthan would be the case with a simple restriction or orifice in the jetpump energizing fuel line.

This has advantages in that there is less power extraction from theengine to drive the fuel pumps, less temperature rise in the fuel, and areduction in weight in the drive gearing to the enginefuel pumps ispermitted. This is accomplished with ease and economy, since the flowresistor is a vortex device with no moving parts and of very simplestructure.

The principal objects of my invention are to achieve the im provementsin fuel systems set out in the preceding paragraph, and particularly toimprove the efficiency and reduce the weight of fuel systems for gasturbine engines.

The nature of my invention and its advantages will be clear to thoseskilled in the art from the succeeding detailed description andaccompanying drawings of the preferred embodiment of the invention.

FIG. 1 is a schematic diagram of a gas turbine engine fuel system;

FIG. 2 is a sectional view of a vortex flow resistor.

Referring to FIG. 1, the engine 2 in the preferred embodiment is assumedto be a gas turbine engine of any usual type, although the fuel systemillustrated is applicable to engines of other sorts. Fuel is supplied tothe engine from a tank or reservoir 3 through a fuel line 4, acentrifugal boost pump 6, a boost pump outlet line 7, a positivedisplacement pressure pump 8, a fuel line 10, a fuel control 11, andan-engine fuel line 12. The fuel control may embody mechanisms of theusual sort for providing control of the power level of the engine andsafeguarding it from overfueling, underfueling, overspeed, and otherhazards. Such fuel controls usually include some sort of manual inputindicated at 14 to regulate engine power level.

In a gas turbine engine, the pressure of the fuel delivered to theengine increases with fuel flow and increases also with increases ofambient pressure. Thus, for example, during full throttle operation atlow altitudes the fuel pressure may be of the order of 1,000 p.s.i.,whereas at low power levels at high altitude the fuel pressure may bemuch less, perhaps 200 p.s.i. The main or pressure pump 8 supplies thefuel at sufiicient pressure to force it into the engine and the boostpump 6 supplies the fuel to the pump 8 at a substantial pressure toavoid cavitation in pump 8. The engine includesan auxiliary drive shaft16 which is connected by the schematically represented gearing to theboost pump 6 through a shaft 18, the main pump 8 through a shaft 19, andthe fuel control 11 through a shaft 20. The engine thus drives the pumpsand provides an input of engine speed to the fuel control for overspeedcontrol and fuel regulation purposes.

The system illustrated is of the sort in which the fuel pump is of afixed displacement type with an output roughly proportional to engine.speed. The fuel pump output must at all times exceed the maximum enginerequirements for any engine rotational speed. Thus, ordinarily, there isan excess of fuel pumped, some of which is returned by the fuel controlthrough a bypass line 22 to the input of the main fuel pump. Some of thefuel delivered by the main pump 8 is also diverted through a jetpumpenergizing fuel line 19 to the high-pressure fuel inlet 24 of thejet pump. The jet pump, as is well known. is a device of the nature ofan injector in which the jet of highpressure fuel from the nozzle orinlet 24 entrains fuel fromthe tank 3 with it and pumps it into the line4 under sufficient pressure to avoid cavitation in the boost pump 6.

The system as so far described may be considered to be conventional. Inthe conventional system the amount of flow through line 19 wouldordinarily be controlled by a fixed orifice or by the size of the jetnozzle 24 or, in general, by means such that the flow through line 19 isproportional to the square root of pressure drop from the pump outlet tothe tank 3. My invention lies in the addition to the conventional systemof a static flow control means or vertex type flow-resistor 26 in thefuel line 19.

The device 26 is a static device; that is, one with no moving parts andone which has the characteristic that the pressure drop due to flowthrough the device is proportional to the rate of flow raised to a powergreater than two. Specifically a desirable exponent may be of the orderof 2.4. The preferred form of such a device is illustrated in FIG. 2.

The flow resistor 26, which will be referred to hereafter as a vortexdevice, comprises a housing 27 which defines a chamber 28 of circular orspiral cross section as illustrated and a tangential or substantiallytangential inlet 30 to the chamber 28 to which the return line 19 isconnected to jet the fuel into the chamber 28 for swirling movementaround the axis of the chamber. The outlet from chamber 28 is through acircular outlet 31 on the axis of the chamber which connects with theline 19 downstream of the vortex device 26. The outlet 31 is notintended as a throttling device in the ordinary senseand is notprimarily a restriction in the line. The resistance to flow comes fromthe swirling movement of the fuel in the chamber 28, the fuel tending topursue a free vortex flow, that is, a flow in which the swirl componentof velocity of the fluid is inversely proportional to the radius. Ofcourse, the velocity departs somewhat from this proportionality as thefuel swirls inward toward the outlet 31 because of frictional losses andviscosity effects but, as is well known, with such a vortex device asubstantial back pressure is developed with the rapidly swirling fuelflowing over the edge of the outlet 31. A device of this sort has apressure drop characteristic which may be expressed as follows: thepressure drop through the device is proportional to the weight of flowper unit time to an exponent which is greater than two, and the value ofwhich depends upon the physical dimensions and velocity of flow enteringthe device. In a specific device which has been calibrated and which isof appropriate size for a moderate sized gas turbine engine of the orderof 5,000 horsepower, the chamber 28 is approximately 6inches in diameterand six-tenth inch in axial length and the outlet is approximatelynine-tenth inch in diameter. With inlets of A- and %-inch diameter theexponent has been found by test to be approximately 2.37. Higher orlower values of the exponent may be arrived at by modification ofdimensions.

The significance of this exponent greater than two may be appreciatedbyconsideration of the operating situation in a fuel system of the sortand described here. If the line 19 were throttled simply by an orificeand we assume a return flow through line 19 of 5,000 pounds per hourwith a pressure drop of 200 p.s.i. there would then be a flow of 1 1,200pounds per hour with a pressure drop of 1,000 psi. This is approximatelythe range of pressures that might be encountered in a typical gasturbine fuel system. Now, assume a vortex device having the exponent2.37 is substituted for the fixed orifice and the vortex device isdesigned for a 200 p.s.i. drop at 5,000 pounds per hour as with theorifice previously mentioned. Flow with 1,000 psi. drop increases onlyto 9,850 pounds per hour. This is a decrease in the return of flow of1,350 pounds per hour or, in other words, a reduction of 22 percent inthe excess flow. The result can be a corresponding reduction in thecapacity of the pumps 7 and 8 and the accessory drive system to operatethe pumps. Also a useful reduction in the power diverted from the engineto operate the fuel system, and a reduction in fuel temperature risewhich is desirable.

The detailed description of the preferred embodiment of my invention forthe purpose of explaining its principles is not to be considered aslimiting or restricting the invention, since many modifications may bemade by the exercise of skill in the art.

-lclaim:

1. A fuel-pumping system for an engine comprising a fuel reservoir, aprimping pump of the jet type in the reservoir, a boost pump supplied bythe jet pump, a pressure pump supplied by the boost pump, the boost andpressure pumps being driven by the engine, an outlet line to the enginesupplied by the pressure pump, fuel control means in the outlet lineeffective to control the rate of supply of fuel to the engine, and areturn line from the pressure pump to the priming pump to supplyoperative fuel to the priming pump; in combination with avortex-cavity-type flow resistor in the return line having a pressuredrop proportional to flow through the resistor raised to an exponentgreater than two.

2. The combination of a fuel-consuming engine, rotary fuelpumping meansdriven by the engine, fuel control means connected between the saidpumping means and the engine effective to control fuel flow to theengine, and means for supplying fuel to the pumping means including afuel reservoir and a jet pump in the reservoir, in combination with anenergizing fuel line from the outlet of the pumping means to the inletof the jet pump and static flow control means in the energizing fuelline having a characteristic AP proportional to W where AP is pressuredrop, W is fuel flow in weight per unit time, and the exponentx has avalue greater than 2.

3. A combination as recited in claim 2 in which the exponent x isgreater than 2.3.

4. A fuel-pumping system for an engine comprising a fuel reservoir, apriming pump of the jet type in the reservoir, rotary fuel-pumping meanssupplied by the priming pump and driven by the engine, an outlet line tothe engine supplied by the rotary pumping means, and a return line fromthe rotary pumping means to the jet-type pump to supply operative fuelto the priming pump; in combination with static flow control means inthe return line having a pressure drop proportional to flow through theflow control means raised to an exponent greater than two.

5. A system as recited in claim 4 in which the static flow control meansis a vortex cavity device with a single inlet and a single outlet, theinlet being tangential and the outlet being axial.

mm: A.

22 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO.3,645,094 Dated Februry 29, 1972 lnvencork's) Alfred M; Suggs It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 2, line 66, "5/8-1nch" should read 3/8-inc'h Column 3, line 22,"primping" should read priming Signed and sealed this 26th day ofDecember 1972.

(SEAL) Attest:

EDWARD M.FLET0HER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof P tents

1. A fuel-pumping system for an engine comprising a fuel reservoir, aprimping pump of the jet type in the reservoir, a boost pump supplied bythe jet pump, a pressure pump supplied by the boost pump, the boost andpressure pumps being driven by the engine, an outlet line to the enginesupplied by the pressure pump, fuel control means in the outlet lineeffective to control the rate of supply of fuel to the engine, and areturn line from the pressure pump to the priming pump to supplyoperative fuel to the priming pump; in combination with avortex-cavity-type flow resistor in the return line having a pressuredrop proportional to flow through the resistor raised to an exponentgreater than two.
 2. The combination of a fuel-consuming engine, rotaryfuel-pumping means driven by the engine, fuel control means connectedbetween the said pumping means and the engine effective to control fuelflow to the engine, and means for supplying fuel to the pumping meansincluding a fuel reservoir and a jet pump in the reservoir, incombination with an energizing fuel line from the outlet of the pumpingmeans to the inlet of the jet pump and static flow control means in theenergizing fuel line having a cHaracteristic Delta P proportional to Wxwhere Delta P is pressure drop, W is fuel flow in weight per unit time,and the exponent x has a value greater than
 2. 3. A combination asrecited in claim 2 in which the exponent x is greater than 2.3.
 4. Afuel-pumping system for an engine comprising a fuel reservoir, a primingpump of the jet type in the reservoir, rotary fuel-pumping meanssupplied by the priming pump and driven by the engine, an outlet line tothe engine supplied by the rotary pumping means, and a return line fromthe rotary pumping means to the jet-type pump to supply operative fuelto the priming pump; in combination with static flow control means inthe return line having a pressure drop proportional to flow through theflow control means raised to an exponent greater than two.
 5. A systemas recited in claim 4 in which the static flow control means is a vortexcavity device with a single inlet and a single outlet, the inlet beingtangential and the outlet being axial.